Seed predation and patterns of fruit production in Asclepias syriaca L.

Seed predation in relation to patterns of pod (and seed) distribution was examined in five samples of the common milkweed (Asclepias syriaca L.), in tests of the "resource-concentration" effect both within- and beween-plants. The proportion of pods in a cluster that were attacked, particularly by the weevil Rhyssomatus lineaticollis, was not consistently related to the number of pods contained in a cluster, the frequency of cluster sizes in a population, or the variance of cluster sizes on a stem. Proportions of pods attacked per stem were not correlated with stem density in one sample and were not associated with stem height in any sample. Large clusters of pods produced more undamaged pods and, by this measure, were more successful than smaller clusters, but there was no tendency in any population for stems to produce the more successful cluster sizes more frequently. Stems producing more clusters of pods also produced more undamaged pods. We found no evidence that weevil predation contributed to the regulation of the distribution of pods among clusters on a stem.